The present invention provides a series of new compounds which we have named "Leustroducsin A", "Leustroducsin B" and "Leustroducsin C". These compounds have the formula (I), shown hereafter. The invention also provides methods of preparing these compounds by fermentation using a microorganism of the genus Streptomyces, and especially a strain of the species Streptomyces platensis, which is also new and also forms part of the present invention. The compounds of the invention have a variety of therapeutic effects, and, thus, the invention also provides compositions and methods of therapy or prophylaxis using these compounds.
The leustroducsins of the present invention are novel compounds which stimulate the production of hematopoietic factors, such as granulocyte colony-stimulating factor (hereinafter abbreviated to "G-CSF") and granulocyte-macrophage colony-stimulating factor (hereinafter abbreviated to "GM-CSF"); they also stimulate the production of nerve growth factor (hereinafter abbreviated to "NGF"); moreover, they exhibit an antifungal effect, e.g. against Tricophyton mentagrophytes.
Various kinds of cytokines having a hematopoiesic activity, such as colony-stimulating factors (hereinafter abbreviated to "CSF"), and several kinds of glycoproteins (generally named the "interleukins") have to date been prepared by the techniques of gene manipulation. These substances have been used clinically in various ways to reduce the adverse side effects commonly caused by cancer chemotherapy and radiotherapy and to block infection. The effectiveness of these substances has recently become clear [Br. J. Cancer 59, 2-5 (1989)].
It has been found that the administration of these factors themselves to humans by various routes results in clear pharmacological effects, which leads to the possible use of these factors in therapy. However, it is thought that these factors are essentially produced in vivo by certain kinds of cells (e.g. lymphocytes, monocytes, fibroblasts, vascular endothelial cells and stromal cells) through a complicated regulatory system, and that they play homeostatic roles in the production of various kinds of blood cells. Accordingly, if these factors are administered without any consideration for the delicate balance of this regulatory mechanism, several side effects may be observed, which may be caused by the imbalance of this regulatory mechanism; examples of such side effects include inflammation at the site of injection, bone pain, fever and rigor.
On the other hand, instead of administering the hematopoietic factors themselves, it might be possible to administer certain substances which are known to stimulate the production of these hematopoietic factors in the body. For example, it is known that interleukin 1 (hereinafter abbreviated to IL-1) and tumor necrosis factor (hereinafter abbreviated to TNF) can induce the production of CSF etc. by various kinds of cells. These factors, however, cannot always act as specific inducers of hematopoietic factors because they also have various other biological activities.
It is also known that various kinds of low-molecular weight immunoactivators, such as lipopolysaccharides (hereinafter abbreviated to LPS) and muramyldipeptides (hereinafter abbreviated to LDP) can produce various kinds of CSF's by activation of monocytes and macrophages. However, it is known that other physiological effects caused by the activation of macrophages, for example the production of monokines such as IL-1 and TNF occurs at the same time, which can result in various side effects, such as fever [Nippon Acta Radiologica 48, (4), 514 (1988)].
Phorbol esters and calcium ionophores are known to induce CSF production synergistically [Kohama et al.: Experimental Hematology 16, 603-608 (1988)], however, they are also known not only to stimulate the production of hematopoietic factors but also to stimulate the production and secretion of the whole of the secreting proteins, including hormones such as insulin [Y. Nishizuka: Science 225, 1365 (1984)].
Although the precise mechanism has not yet been clarified, it is thought that, in the formation of blood cells, various kinds of mature blood cells can be formed from common cell precursors, called hematopoietic stem cells, through the action of various hematopoietic factors and through cell to cell interaction. It has been established that the site where blood cells are formed in normal adults is limited only to the inside of the bone marrow, that cells called stromal cells existing in the bone marrow play an important role in formation of blood cells [Dexter et al.: J. Cell. Physiol. 91, 335 (1977)], and that stromal cells in the bone marrow produce various hematopoietic factors [Harigaya et al.: Proc. Natl. Acad. Sci. USA 82, 3477 (1985); Kohama et al.: Experimental Hematology 16, 603-608 (1988)].
Therefore, if a substance which stimulates the production of hematopoietic factors by stromal cells can be found, this substance may not only play a very important role in analyzing the action of the hematopoietic mechanism in physiological conditions and in the pathology of hematologic diseases but it may also find considerable clinical use.
European Patent Publication No. 329 361 discloses certain new 2-pyranone derivatives which resemble the compounds of the present invention except that they differ in the nature of the group "R", defined hereafter. Those prior art compounds are also only said to be agricultural biocides and are not shown in the published art to have the valuable and unexpected therapeutic and prophylactic activities of the compounds of the present invention. Although the prior art compounds are produced, like the compounds of the present invention, by a microorganism of the species Strepomyces platensis, the strain described in the prior document is believed to be clearly different from that described herein.
Very similar compounds and microorganisms, having essentially the same disclosed utility, are described in Japanese Patent Application Kokai Hei 2-186, and these are likewise thought to be clearly distinct from the compounds and microorganism disclosed herein. The Journal of Antibiotics, Vol. XLII, No. 9, page 331 discloses a novel antitumor compound, which the authors call "Phospholine", and which is produced by a microorganism of the genus Streptomycet, which was then newly isolated. However, the microorganism is clearly said to be Streptomyces hygroscopicus and is distinguished from the Streptomyces platensis, which is used in the present invention. Moreover, although the prior art phospholine, like the compounds of the present invention, has both an amino group and a phosphoric group, it has a different molecular formula is thus clearly distinguished.